⚠️ Breaking Change in v1.19: default UID Changed

### Description

Starting from version 1.19, the default UID (User ID) of the fluent user in `vX.Y-A` and `vX.Y.Z-A.B` images has been changed.
This update may cause Permission denied errors if you are mounting host directories or volumes that rely on the previous UID.

If you encounter permission issues,
please update the ownership of your host directories to match the new UID,
or explicitly specify the user when running the container (e.g., using the -u option).

Please refer to https://github.com/fluent/fluentd-docker-image/issues/448 for details.

### Status

Since v1.19 has already been released, making changes would cause further confusion.
So this is a design specification for now...

Start by reading issue #448 and the v1.19 image context referenced here. Confirm whether any documentation change is still requested; done would require a specific, versioned migration or UID note, since this issue says v1.19 is already released and proposes no code changes.

Written by the indexing model from the issue text.